Using Pockets for positioning....
-
- Vectric Craftsman
- Posts: 148
- Joined: Sun Jul 24, 2016 5:40 pm
- Model of CNC Machine: Axiom AR4 V5 Pro
- Location: Colorado
Using Pockets for positioning....
I am trying to cut mortise pockets and, the tenons (rabbits) to match, on small components of a box. So I start out by pocketing a piece of MDF with the pockets the size of each part that has the mortise or tenon cut in it. Easy enough to calculate the tool path for this. Do you have to pocket the full thickness of your material? What if you only pocket down 1/8 inch or just enough to position the part? (with a small piece to DS tape) Do you keep the same tool paths but just set Z for the new thickness since the parts protrude above the pocket board? Some pieces need to be flipped for machining on both sides so the pockets would help positioning for multiple parts. I have always done this on a router table but with my new CNC I think this could be a lot faster and easier, if I knew how to do it. I am talking about small box parts that are in the 3"X 3"x 5/8" range of size. Maybe this is more trouble than it is worth. What do you think.
- dhellew2
- Vectric Wizard
- Posts: 1326
- Joined: Thu May 22, 2008 10:14 pm
- Model of CNC Machine: Legacy Artisan 72 and AVID CNC Rotary
- Location: Royal City Washington
Re: Using Pockets for positioning....
You can cut pockets to any depth you want.
To cut on both sides you should use guide pins so when the part is flipped over it will be in the exact alignment position.
You can clamp a spoil board to your table so you don't cut through your table.
Everyone has their preferences... some like pins so the part can only be flipped one way along the desired axis.
I like 2 pins one on each end along the x-axis located at the part center along the y-axis.
Drill the pin holes first through the part into the spoil board, insert the pins, then carve your part.
I typically use 3/16" dowels but sometimes depending on the size of the part, as big as 1/2".
When carving a 3.5" thick x 25" wide x 42" tall headstone I used 1/2" pins.
To cut on both sides you should use guide pins so when the part is flipped over it will be in the exact alignment position.
You can clamp a spoil board to your table so you don't cut through your table.
Everyone has their preferences... some like pins so the part can only be flipped one way along the desired axis.
I like 2 pins one on each end along the x-axis located at the part center along the y-axis.
Drill the pin holes first through the part into the spoil board, insert the pins, then carve your part.
I typically use 3/16" dowels but sometimes depending on the size of the part, as big as 1/2".
When carving a 3.5" thick x 25" wide x 42" tall headstone I used 1/2" pins.
You will get old if you live long enough!
Young = time, no money
Old = money, no time
Dale
Young = time, no money
Old = money, no time
Dale
- martin54
- Vectric Archimage
- Posts: 7353
- Joined: Fri Nov 09, 2012 2:12 pm
- Model of CNC Machine: Gerber 48, Triac PC, Isel fixed gantry
- Location: Kirkcaldy, Scotland
Re: Using Pockets for positioning....
What control software are you using for your cnc machine?
I use mach3 which allows you to set up work co ordinates for doing repeat work. I have made most of my jigs from ply mainly because I was worried that over time mdf would warp/swell with moisture. My unit isn't the driest warmest place in the winter
The jigs were cut on the cnc & have dowel holes which fit into the spoilboard, means I can put the jig on the table in exactly the same place every time & then using the right work co ordinates my x & y zero is always set to the same place.
I have cut my pockets all the way through the ply but they probably don't need to be that deep, I wouldn't think 1/8" would be deep enough though, mine are deep enough that they aid holding the part as well as aligning it, with an 1/8" pocket you would be relying on just the tape for hold down unless you intend using clamps as well which means you cant machine the whole surface of your part
I use the same file all the time, I just open it, alter the material thickness & then recalculate the toolpaths, you will get a message about recalculating toolpaths if you alter anything on the material set up page which is handy as it means you can't forget to do it
If I need to change any of the artwork I will do that & then save the file as a different name & keep the original as it was. I set my z axis from the top of the material because that is just the way I have always worked but you could set it from the table/material bottom so your z 0 would always be in the same place regardless of material thickness.
As with most things it depends on what you are doing, it will take time to set up the files & cut your jig so for a one off it might not be worth spending the time to do it but if this is something you do fairly regularly then once you have done the initial work every other one is pretty quick to do
I use mach3 which allows you to set up work co ordinates for doing repeat work. I have made most of my jigs from ply mainly because I was worried that over time mdf would warp/swell with moisture. My unit isn't the driest warmest place in the winter
The jigs were cut on the cnc & have dowel holes which fit into the spoilboard, means I can put the jig on the table in exactly the same place every time & then using the right work co ordinates my x & y zero is always set to the same place.
I have cut my pockets all the way through the ply but they probably don't need to be that deep, I wouldn't think 1/8" would be deep enough though, mine are deep enough that they aid holding the part as well as aligning it, with an 1/8" pocket you would be relying on just the tape for hold down unless you intend using clamps as well which means you cant machine the whole surface of your part
I use the same file all the time, I just open it, alter the material thickness & then recalculate the toolpaths, you will get a message about recalculating toolpaths if you alter anything on the material set up page which is handy as it means you can't forget to do it
If I need to change any of the artwork I will do that & then save the file as a different name & keep the original as it was. I set my z axis from the top of the material because that is just the way I have always worked but you could set it from the table/material bottom so your z 0 would always be in the same place regardless of material thickness.
As with most things it depends on what you are doing, it will take time to set up the files & cut your jig so for a one off it might not be worth spending the time to do it but if this is something you do fairly regularly then once you have done the initial work every other one is pretty quick to do
-
- Vectric Craftsman
- Posts: 148
- Joined: Sun Jul 24, 2016 5:40 pm
- Model of CNC Machine: Axiom AR4 V5 Pro
- Location: Colorado
Re: Using Pockets for positioning....
Thanks a lot for the info guys. I am using Vcarve for my machine software. My Axiom has a spoil board set up in strips on the aluminum table so maybe I could fashion some type of T-track positioning with some knobs to put the pocketing board on top of the strips that would always be in the same position. That way I could drill into the pocket board with dowels using jigs for various projects. Does that seem like a plan? BTW if you are cutting the pockets with end mills to put square parts in I am assuming you need to chisle out the corners, right.....
- FixitMike
- Vectric Wizard
- Posts: 2177
- Joined: Sun Apr 17, 2011 5:21 am
- Model of CNC Machine: Shark Pro Plus (retired)
- Location: Burien, WA USA
Re: Using Pockets for positioning....
For square parts you can use dogbone fillets so the corners will clear.
Good judgement comes from experience.
Experience comes from bad judgement.
Experience comes from bad judgement.
-
- Vectric Craftsman
- Posts: 148
- Joined: Sun Jul 24, 2016 5:40 pm
- Model of CNC Machine: Axiom AR4 V5 Pro
- Location: Colorado
Re: Using Pockets for positioning....
Ah Ha...... thank you. I am slowly catching on..
- martin54
- Vectric Archimage
- Posts: 7353
- Joined: Fri Nov 09, 2012 2:12 pm
- Model of CNC Machine: Gerber 48, Triac PC, Isel fixed gantry
- Location: Kirkcaldy, Scotland
Re: Using Pockets for positioning....
I just square out the corners with a file, your not removing a lot of material so only takes a few seconds, could use fillets as Mike has suggested but when I made most of the jigs I am using I didn't think to do that
You will need to make your pockets fractionally larger than the parts that will fit into them but do this in very small stages or you will end up with a very sloppy fit which will allow the parts some movement in the jig.
This tutorial is about 2 sided machining but they use a jig for alignment.
http://support.vectric.com/tutorials/V8 ... rts_2.html
There is also a video by Andrew Pitts somewhere where he makes a jig that uses a wedge shaped piece to lock the parts in place but I can't seem to find it just now.
You will need to make your pockets fractionally larger than the parts that will fit into them but do this in very small stages or you will end up with a very sloppy fit which will allow the parts some movement in the jig.
This tutorial is about 2 sided machining but they use a jig for alignment.
http://support.vectric.com/tutorials/V8 ... rts_2.html
There is also a video by Andrew Pitts somewhere where he makes a jig that uses a wedge shaped piece to lock the parts in place but I can't seem to find it just now.
- SteveNelson46
- Vectric Wizard
- Posts: 2310
- Joined: Wed Jan 04, 2012 2:43 pm
- Model of CNC Machine: Camaster Stinger 1
- Location: Tucson, Az.
Re: Using Pockets for positioning....
On You Tube, its the one where he makes a dish. Here is the link.martin54 wrote:I just square out the corners with a file, your not removing a lot of material so only takes a few seconds, could use fillets as Mike has suggested but when I made most of the jigs I am using I didn't think to do that
You will need to make your pockets fractionally larger than the parts that will fit into them but do this in very small stages or you will end up with a very sloppy fit which will allow the parts some movement in the jig.
This tutorial is about 2 sided machining but they use a jig for alignment.
http://support.vectric.com/tutorials/V8 ... rts_2.html
There is also a video by Andrew Pitts somewhere where he makes a jig that uses a wedge shaped piece to lock the parts in place but I can't seem to find it just now.
Steve
-
- Vectric Craftsman
- Posts: 148
- Joined: Sun Jul 24, 2016 5:40 pm
- Model of CNC Machine: Axiom AR4 V5 Pro
- Location: Colorado
Re: Using Pockets for positioning....
Thanks for the great information....I really like the idea of the wedge jig. I have a lot to learn. Seems like the possibilities are endless.
- adze_cnc
- Vectric Wizard
- Posts: 4379
- Joined: Sat Jul 27, 2013 10:08 pm
- Model of CNC Machine: AXYZ 4008
- Location: Vancouver, BC, Canada
Re: Using Pockets for positioning....
Poor rabbits just hopping along minding their own business and along comes some rascally woodworker out to cut them.zaxis wrote:I am trying to cut mortise pockets and, the tenons (rabbits) to match
That's why I call "rabbets" rebates, as the English do, so there's no confusion with bunnies---just confusion with getting money back on the purchase of consumer goods.
-
- Vectric Wizard
- Posts: 447
- Joined: Thu Oct 02, 2014 1:49 pm
- Model of CNC Machine: FMT Patriot 4 x8
Re: Using Pockets for positioning....
I use pockets often to position and hold parts with the aid of my vacuum pump. One added benefit of pockets can be controlling tearout. If you have cuts coming through end grain, having the workpiece supported by a full depth pocket helps to reduce tearout.
Another point, pockets for positioning need not be a fully surrounding piece. I will screw down blocks just inside the intended position of the workpiece prior to running a profile pass to establish the part outline.
If you make yourself some standard wedges from Russian birch ply you can drop the wedge design into your project drawings when needed.
Another point, pockets for positioning need not be a fully surrounding piece. I will screw down blocks just inside the intended position of the workpiece prior to running a profile pass to establish the part outline.
If you make yourself some standard wedges from Russian birch ply you can drop the wedge design into your project drawings when needed.